My speedqueen dryer tumbles,but no heat or air flow.?

The igniter turns red(heats up) and the gas turns on for about 2 seconds,then shuts off. The tumbler keeps rotating,the gas line has no kinks,etc. ? But there is no exhaust out the back of the dryer. tried vacuuming it,not sure if I got everything,or if there are more than one moter supossed to be running(tumbler motor,exhaust moter???) Seems like the exhaust moter(if there is such a thing) doesn`t draw the heat through the system,so the thermostat(heat switch) shuts the gas off,not sure,any ideas??